Platform-Provided Behaviors for Custom Elements

[anaskim]

Specification

Explainer: https://github.com/MicrosoftEdge/MSEdgeExplainers/blob/main/PlatformProvidedBehaviors/explainer.md
WHATWG issue: whatwg/html#12150

Description

This feature introduces "Platform-Provided Behaviors" to ElementInternals, allowing custom elements to adopt native behaviors without extending native elements or reimplementing complex logic. It modifies attachInternals to accept a list of behaviors, starting with HTMLSubmitButtonBehavior, which wires up form submission on activation.

Documentation

https://github.com/MicrosoftEdge/MSEdgeExplainers/tree/main/PlatformProvidedBehaviors

Browser support

Chromium: Positive, prototyping - Chrome Platform status entry
Mozilla: No signal mozilla/standards-positions#1380
WebKit: No signal WebKit/standards-positions#642

[ddbeck]

Thanks for filing this issue, @anaskim. I'm going to take some notes here to help eventually author the feature entry here. A review of this for accuracy would be welcome, but not required. Thanks again!

Name and ID

There's a general concept here ("platform-provided behaviors") but a more narrowly scoped implementation effort here (i.e., HTMLSubmitButtonBehavior). This suggests to me that we'd start with the narrow bit first, with an ID like htmlsubmitbbuttonhavior and a name like "Submit button behavior for custom elements".

Then, when/if more behaviors appear, we'd add a higher-level group or feature ("Platform-provided behaviors…") that the individual behaviors will join or someday merge into.

Description

In our style, something like:

An HTMLSubmitButtonBehavior object, attached to a custom element with the behaviors option to attachInternals(), adds to a custom element the built-in submit button behaviors, such as keyboard focus and submission, ARIA role, and CSS pseudo-class matching.

Compat data

Based on the explainer, I'd expect to see the following mdn/browser-compat-data keys:

api.HTMLSubmitButtonBehavior
api.HTMLSubmitButtonBehavior.HTMLSubmitButtonBehavior # constructor
api.HTMLElement.attachInternals.options_parameter.behaviors

This is likely incomplete. I imagine there will be a bunch of properties on HTMLSubmitButtonBehavior objects (from the explainer, formAction). Without an IDL, I can't easily speculate on what those keys might be.

[captainbrosset]

See also:

• https://bsky.app/profile/patrickbrosset.com/post/3mlljob6ub22y
• https://mas.to/@patrickbrosset/116556512460138797